A sterilization treatment using peroxide as a pasteurization agent or a sterilization agent illustrated with ozone, hydrogen peroxide and peracetic acid has been carried out in a food field or a medical field in which harmless and clean production circumstances and hygiene managements are required. As thus chemical sterilization treatment methods, it is known to carried out a low-temperature sterilization method such as a gaseous sterilization method using a gas illustrated with an ozone gas and an ethylene oxide gas having a sterilizing activity, or a low-temperature plasma sterilization method using a sterilization activity by low-temperature plasma which is prepared through plasma activation of a gas illustrated with a hydrogen peroxide gas having an oxidizing activity. The low-temperature sterilization methods are capable of going through sterilization at low-temperature in a short time as compared to a high-temperature steam sterilization method using a high temperature and pressure aqueous vapor in an autoclave. The low-temperature sterilization methods are useful for sterilizing plastic products for which an autoclave is unable to be used. Therefore the low-temperature sterilization methods have been prevalent.
A discoloration indicators are used for indicating or affirming through change of hue whether the sterilization treatment were completed or not, or were effectively carried out or not. The discoloration indicators are required to change color according to conditions such as concentration of a sterilization agent or a pasteurization agent, and duration time of exposure thereof during sterilization treatment procedures.
For example, Patent Document 1 discloses an indicator for plasma sterilization comprising an azo dye, a compound as an auxiliary color coupler having a mercapto group or a dithiocarbamyl group, and a resin as a binder. A polyphenol compound or an aromatic carboxylic acid for development by the auxiliary color coupler is added thereto to prevent decomposition or disappearing of the azo dye during the sterilization treatment or color deterioration under high humidity after the discoloration. It discloses an exemplified indicator which changes from red to blue.
Patent Document 2 discloses an indicator for oxidative sterilization which utilises producing a development compound through reacting a primary amine with an aldehyde to evaluate effectivity of an sterilization process. According to this indicator, after either one of the primary amine and an aldehyde is kept away a pasteurization agent from reacting each other and another one is kept to be encapsulated in an ampule, the ampule is fractured and then both of them are contact each other in conducting the sterilization treatment in order to color. An exposure amount of the pasteurization agent such as hydrogen peroxide, peracetic acid, ethylene oxide, ozone, chlorine dioxide and the like is estimated by intensity of coloring thereof.
Thus pasteurization agent or sterilization agent used for the sterilization treatment behaves to be a gaseous phase. They are so toxic that human may be damaged. Therefore it is required to monitor or detect the concentration of those gases. As an indicator for detecting the gas, Patent Document 3 discloses an indicator for detecting an oxidative gas comprising at least one selected from the group consisting of an azo dye, a methine dye, triarylmethane dye, a thiazine dye. The indicator may include a cationic surface-activating agent as an auxiliary color coupler, silica as an extender pigment and an anthraquinone dyestuff as a dye respectively.
And as an indicator having a discoloration rate according to concentration of a hydrogen peroxide gas, Patent Document 4 discloses an indicator for detecting a hydrogen peroxide gas comprising a styrene-acrylic resin and/or a styrene-maleic resin and a methine dye. The indicator may include a cationic surface-activating agent as an auxiliary color coupler, and silica as an extender pigment.
Various indicators, which are best suited to detecting those sterilization treatments or gases, has been sold. However, as of now there are few indicators which are satisfied with preservation stability and visible distinguishability due to using an organic compound as a discoloration component such as an organic dyestuff. The indicators including the organic pigment tend to cause color deterioration because the pigments such as the included dyestuff and the like are decomposed by light. Furthermore the indicators have poor visible distinguishability and are difficult to evaluate an intermediate discoloration point, because hue changes from a chromatic color to other chromatic color or changes between close color. Especially unfamiliar operators are hard to instantaneously estimate whether the hue changes completely or not.